Absorbent product including absorbent layer treated with surface active agent

ABSTRACT

An absorbent product comprising a liquid permeable surface sheet, a liquid nonpermeable back sheet and an absorbent layer located therebetween, wherein the absorbent layer comprises a water nonswellable synthetic fiber (a) and optionally cellulose fiber (b), and a water-absorbent resin (c), with the weight ratio of (a):(b) being (100 to 20):(0 to 80) and the percentage content of (c) based on the weight sum of (a), (b) and (c) is 25 to 75 weight %. The absorbent layer is treated with polyoxyalkylene-modified silicone surface active agent (d1) and/or a nonsilicone surface active agent having HLB of 8 to 14 (d2). Absorbent products of the present invention exhibit excellent shape retention in the moist state and good permeability and diffusibility for the absorbed liquid. Accordingly, they provide excellent surface dryness, reduced leakage and thus can be comfortably used for a long time and effectively applied to disposable diapers, sanitary napkins and incontinence pads.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to disposable absorbent products such asdisposable diapers, sanitary napkins and incontinence pads. Morespecifically, it relates to absorbent products exhibiting excellentpermeability and diffusibility of the absorbed liquid in the absorbentlayer without leakage, thereby providing good dryness and comfort to theuser.

2. Description of the Prior Art

Hitherto, various proposals have been advocated for absorbent products'properties aimed at improving the absorption rate of urine or blood,improving the dryness after absorption, or reducing leakage.

Most of such proposals relate to improvement of the liquid permeablesurface sheet or surface nonwoven fabric (as disclosed in the officialgazette notice for JP-A-58-60068, the official gazette notice forJP-A-1-148879 and the official gazette notice for JP-A-2-169774), use ofwater-absorbent resins having a specific performance or property,disposition of an absorbent resin in the absorbent layer, use of ahydrophilic diffusion layer comprising a nonwoven fabric or awater-absorbent paper, and an embossing method for the absorbent layer.Thus few improvements concerning the absorbent layer itself containingan absorbent resin have been proposed so far. This is becauseconventional disposable diapers have an absorbent layer made ofmaterials with a high hydrophilic property, such as fluff pulp, waterabsorbent paper and water absorbent resin.

These days, with the property improvement of absorbent products such asdisposable diapers and sanitary napkins, such products tend to be usedover a long time. Further, as to disposable diapers, as they becomethinner, the ratio of water absorbent resin/fiber substrate thereintends to become greater. On the other hand, satisfactory shape retentionor unity of the water absorbent resin/fiber substrate can not beobtained with an absorbent layer comprising a water-absorbent resin anda conventional cellulose fiber such as fluff pulp and water absorbentpaper, regardless of the application of the water-absorbent resin,namely, whether in a method of sandwiching between pulp layers or waterabsorbent papers, or in a method of mixing with pulp. That is,hydrophilic cellulose fibers that absorb and retain liquid such as urineand blood by physical capillary action have problems such assusceptibility to deformation by an external force such as the wearer'smovement during a period of water absorption or after water absorptionto ruin the unity of the water absorbent resin/fiber substrate, whichlead to leakage and deterioration of dryness.

Proposals to prevent deformation of absorbent layers in the wet state,that is, to provide resilience to enable restoration of the absorbentlayer when an external force such as compression and distortion isapplied thereto, have been made. For example, an attempt has been madeto form an absorbent layer by sandwiching a water absorbent resinbetween sheets comprising a synthetic fiber. Although this method canimprove shape retention in the wet state to some degree, it causes aproblem in that when the amount of the water absorbent resin issufficiently large, the water absorbent resin sandwiched between thefiber sheets forms a gel layer after absorption, and the gel layer canbe displaced by an external force to ruin the unity between the waterabsorbent resin gel/fiber substrate and cause leakage. Further, sincesynthetic fibers are not hydrophilic, a problem or deterioration of thepermeability and the diffusibility of the liquid occurs.

Moreover, a proposal has been made to improve shape retention of theabsorbent layer by mixing and dispersing water-absorbent resin in afiber substrate which is a combination of a heat-adhesive syntheticfiber and fluff pulp with heat treatment. However, although this methodprovides improvement of shape retention, since the hydrophilic propertyof the absorbent layer deteriorates as the ratio of the synthetic fiberincreases, a problem of deterioration of the liquid's permeability ordiffusibility occurs as compared with a conventional absorbent layerconsisting of cellulose fiber.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provideabsorbent products that have excellent shape retention and unity ofwater-absorbent resin/fiber substrate even in a wet state, good liquidpermeability and diffusibility without leakage and excellent surfacedryness after absorption, and that can remain comfortable over a longperiod of use.

That is, the present invention provides an absorbent product comprisinga liquid permeable surface sheet, a liquid nonpermeable back sheet andan absorbent layer located therebetween, wherein the absorbent layercomprises a water nonswellable synthetic fiber (a) or the syntheticfiber (a) and a cellulose fiber (b), and a water-absorbent resin (c).The weight ratio of (a):(b) is (100 to 20):(0 to 80) and the percentagecontent of (c) based on the weight sum of (a), (b) and (c) is 25 to 75weight %. The absorbent layer is treated with a polyoxyalkylene-modifiedsilicone surface active agent (d1). The present invention also providesan absorbent product comprising a liquid permeable surface sheet, aliquid nonpermeable back sheet and an absorbent layer locatedtherebetween, wherein the absorbent layer comprises a water nonswellablesynthetic fiber (a) or the synthetic fiber (a) and a cellulose fiber(b), and a water-absorbent resin (c). The weight ratio of (a):(b) is(100 to 20):(0 to 80) and the percentage content of (c) based on theweight sum of (a), (b) and (c) is 25 to 75 weight %. The absorbent layeris treated with s nonsilicone surface active agent having HLB of 8 to 14(d2).

DETAILED DESCRIPTION OF THE INVENTION

Examples of water non-swellable synthetic fibers (a) in the presentinvention include thermoplastic fibers of polyolefin fibers such aspolyethylene fibers, polypropylene fibers, polyethylene-polypropyleneconjugate fibers; polyester fibers such as polyethylene terephthalatefibers, polyethylene terephthalate-polyethylene isophthalate copolymerconjugate fibers; polyolefin-polyester conjugate fibers, polyamidefibers and polyacrylonitrile fibers.

Among these examples of synthetic fibers, polyolefin fibers, polyesterfibers and conjugate fibers thereof are preferable. Further, sheath &core type, eccentric core-sheath type and side-by-side typeheat-adherent conjugate polyolefin fibers are preferable with respect toapplicability to disposable diapers as having excellent shape retentionproperty after liquid absorption.

The length and diameter of the above mentioned synthetic fibers are notparticularly limited and in general, any one having a length of 1 to 200mm and a diameter of 0.1 to 100 denier can be preferably used. Shape isnot particularly limited and examples include web type, narrow cylindertype, cut split yarn type, staple fiber type and filament type.

Examples of cellulose fibers (b) optionally used include those used inconventional absorbent products such as fluff pulp and cotton type pulp.The materials, such as coniferous and deciduous tree, and productionmethods, such as chemical pulp, semichemical pulp, chemithermomechanical pulp (CTMP) and bleaching method, are not particularlylimited.

The weight ratio of (a):(b) is in general, (100 to 20):(0 to 80),preferably (100 to 25):(0 to 75), and more preferably (100 to 30):(0 to70). If the amount of (a) is less than 20 weight %, shape retention ofthe absorbent layer deteriorates. Consequently, when an external forceis applied to the absorbent layer by the user's movements at or afterliquid absorption to compress or twist the absorbent layer, leakage ordryness deterioration would occur.

Examples of water-absorbent resins (c) of the present invention includecrosslinked copolymers of starch-acrylic acid salt, crosslinkedpolyacrylic acid salt, self-crosslinked polyacrylic acid salt,saponified crosslinked copolymers of acrylate ester-vinyl acetate,crosslinked copolymers of isobutylene-maleic anhydride, crosslinkedpolysulfonic acid salt, derivatives of modified cellulose andcrosslinked polyethylene oxide. Hydrophilic crosslinked polymerscontaining acrylic acid salt and/or acrylic acid as the main monomercomponent of the polymer are more preferable with respect to capabilityof absorbing and retaining large amounts of liquid by ion osmoticpressure, and unsusceptibility to liquid discharge even when a load orexternal force is applied. The kinds of these salts are not particularlylimited, but in general, alkaline metal salts such as sodium andpotassium are used.

Further, resins prepared by crosslinking the surface of a powdery waterabsorbent resin can be preferably used in the present invention. Unlikewater-soluble resins, water-absorbent resins are water-insoluble andwater-swellable.

Among the water-absorbent resins (c), those having an absorbency under apressure-free state to physiological saline of 40 g/g or more, anabsorbency under loading of 20 g/g or more and a gel elastic modulus of20,000 dyne/cm² or more are preferable. Those having an absorbency undera pressure-free state of 45 to 75 g/g, an absorbency under loading of 25to 50 g/g and a gel elastic modulus of 30,000 to 200,000 dyne/cm² aremore preferable. Those having an absorbency under a pressure-free stateof 50 to 75 g/g, an absorbency under loading of 35 to 50 g/g and a gelelastic modulus of 35,000 to 200,000 dyne/cm² are further preferable.

It is economical to use a water-absorbent resin having an absorbencyunder a pressure-free state of 40 g/g or more, since sufficientabsorption property can be obtained with only a small amount of thewater-absorbent resin. Further, it is economical to use awater-absorbent resin having an absorbency under loading of 20 g/g ormore, since sufficient absorption property can be obtained with only asmall amount of the water-absorbent resin. It is preferable to use awater-absorbent resin having a gel elastic modulus of 20,000 dyne/cm² ormore, since the swelled gel after absorption does not become too soft,is not liable to be deformed by load or external force, and particles ofthe swelled gel are not liable to stick to each other to cause blockingor prevent permeation or diffusion of liquid.

Absorbency under pressure-free state, absorbency under loading and gelelastic modulus are measured by the following methods.

Absorbency under pressure-free state:

1 g of the water absorbent resin was placed in a 10 cm×20 cm sizetea-bag prepared with 250-mesh nylon net and immersed in an excessamount of a physiological sodium chloride solution (concentration: 0.9wt %) for 30 minutes. Then it was removed, drained of excess solutionfor 15 minutes, and measured for an increase of weight. The value wasdefined as water absorbency under pressure-free state.

Absorbency under loading:

In s cylindrical plastic tube (30 mm in inside diameter, 60 mm high)with a 250-mesh nylon net affixed on the bottom surface, 0.1 g of thewater absorbent resin was placed and uniformly spread over the nylonnet, on which a weight (30 mm in outside diameter) was placed so that a20 g/cm² load was applied. A tube containing the water absorbent resinwas immersed in a Petri dish (12 cm in diameter) containing 60 ml of thephysiological sodium chloride solution, and left standing with the nylonnet side down for 30 minutes. The 10-fold value of the increase inweight after 30 minutes of absorption was defined as water absorbencyunder loading.

Gel elastic modulus:

40 ml of artificial urine was added to 1 g of water-absorbent resin toform a 40 fold absorption gel. 0.1 g of the gel was placed in the centerof the supporting table of a creep meter manufactured by YAMADEN Co.,Ltd. Then a cylinder was lowered from the upper direction to compressthe gel to 0.3 mm thickness. The stress (F) at the time of compressionand the sectional area (S) of the compressed gel were measured tocalculate the stress at the time of compression per a unit area by thefollowing formula. And the value was designated as the gel elasticmodulus.

    Gel elastic modulus (dyne/cm.sup.2)=(F×980)/S

The shape of a water absorbent resin (c) is not particularly limited andboth powdery and fibrous forms can be used preferably. Preferableexamples include powders such as particle, granulate, agglomerate,lameliar, massive and spherical.

When the water absorbent resin is powdery, the average particle size isabout 150 to 700 μm, preferably 200 to 600 μm, and more preferably 250to 500 μm. Powders of a water-absorbent resin having an average particlesize of 150 μm or more are preferable with respect to unsusceptibilityof gel blocking in the case of contacting a liquid. It is furtherpreferable with respect to the unsusceptibility the water absorbentresin from falling out of the absorbent layer. On the other hand, sincethe water absorption rate becomes drastically slow if the averageparticle size exceeds 700 μm, an average particle size of 700 μm or lessis preferable. Further, since an average particle size of 700 μm or lessdoes not provide an uncomfortable feel due to coarseness of theparticles in the surface of a disposable diaper, nor the problem ofbreakage of the back sheet by coarse particles, it is preferable.

The ratio of water absorbent resin (c) in the present invention based onthe sum of the weight of (a), (b) and (c) is 25 to 75 weight %,preferably 30 to 70 weight %, and more preferably 35 to 70 weight %.

If the ratio of (c) is less than 25 weight %, since a synthetic fiber(a) does not have a swellable property by water absorption, theabosrbent layer needs to be thick to secure a sufficient absorptioncapacity, and thus a thin product can not be provided. On the otherhand, if the ratio of (c) exceeds 75 weight %, unity of the waterabsorbent resin and the fiber substrate can not be secured.

The amount of a water-absorbent resin (c) per one water-absorbentproduct is not particularly limited. For example, the amount for adisposable diaper is in general 5 to 20 g. The amount for a thin-typediaper is in general, 7 to 20 g, preferably 8 to 20 g. On the otherhand, if the amount exceeds 20 g, a great amount of fiber substrate isrequired in order to secure the unity of the water absorbent resin andthe fiber substrate, which is uneconomical. Unlike the above mentionedembodiment of disposable diapers, when an absorbent product is used forsanitary napkins or incontinence pads, the amount may be smalleraccording to the application and the size of the product.

In the present invention, polyoxyalkylene modified silicone surfaceactive agents (d1) and/or nonsilicone surface active agent having HLB of8 to 14 (d2) are used as a surface active agent. The term "surfaceactive agent (d)" is used generically when both of them are referred tohereinafter.

Among the surface active agents (d), examples of polyoxyalkylenemodified silicone surface active agents (d1) include polyoxyethylenemodified dimethyl polysiloxane, dimethyl polysiloxane modified withblock or random copolymers of polyoxyethylene-polyoxypropylene,dimethylpolysiloxane modified by polyoxyethylene having an end alkylgroup of 1 to 12 carbon atoms, dimethylpolysiloxane modified with blockor random copolymers of polyoxyethylene-polyoxypropylene having an endalkyl group of 1 to 12 carbon atoms, and dimethyl polysiloxanederivatives which are dimethyl polysiloxane having an amino group or anepoxy group at the end and/or in the molecule modified with the abovementioned polyoxyalkylene. Among these examples, polyoxyethylenemodified dimethyl polysiloxane and dimethylpolysiloxane modified withblock or random copolymers of polyoxyethylene-polyoxypropylene arepreferable, and polyoxyethylene modified dimethyl polysiloxane isfurther preferable with respect to the availability at a low price.

The molecular weight of polyoxyalkylene-modified silicone surface activeagents (d1) is not particularly limited, and in general, is 500 to10,000, preferably 500 to 5,000, and more preferably 500 to 3,000. Ifthe molecular weight is 500 or more, since the treatment with a greatamount of (d) is not required in order to achieve good permeability anddiffusibility of a liquid in the absorbent layer, it is economical.Further, if the molecular weight is 10,000 or less, since the viscositywould not be too high, a uniform treatment can be facilitated.Accordingly, since an extremely great amount of solvent is not requiredin order to adjust (d1) to an appropriate viscosity and thus the processof eliminating the solvent is not particularly required, it isefficient.

The percentage content of a polyoxyethylene group of apolyoxyalkylene-modified silicone surface active agent (d1) can varyaccording to the degree of desired water affinity, and in general it is25 to 75 weight %, preferably 30 to 70 weight %, and more preferably 40to 60 weight %. The ratio of an oxyethylene group and an oxypropylenegroup is not particularly limited as long as the percentage content of apolyoxyethylene group is in the above mentioned range, and in general is(100 to 50):(0 to 50), preferably (100 to 60):(0 to 40). It ispreferable that the percentage content of a polyoxyethylene group is 25weight % or more, since the water affinity would not deteriorate, and agood permeability and diffusibility of a liquid are secured in treatingthe absorbent layer. Further, it is preferable that the percentagecontent of a polyoxyethylene group is 75 weight % or less, since thewater solubility would not become too strong and the permeability anddiffusibility of a liquid in repetitive absorptions can be maintained.

Examples of nonsilicone surface active agents having HLB of 8 to 14 (d2)include ethyleneoxide adducts of higher alcohols such as polyoxyethyleneoleylether, polyoxyethylene cetylether and polyoxyethylene laurylether;ethylene oxide adducts of alkylphenol such as polyethylenenonylphenylether; polyoxyethylene monoaliphatic acid esters such aspolyoxyethylene monooleate, polyoxyethylene monostearate andpolyoxyethylene monolaurate; polyethylene glycol dialiphatic acid esterssuch as polyoxyethylene dioleate, polyoxyethylene distearate andpolyoxyethylene dilaurate; ethylene oxide adducts of partial esters ofpolyhydric alcohol with aliphatic acid such as sorbitan monooleate (EO 5mole), sorbitan monostearate (EO 4 mole), sorbitan monolaurate (EO 4mole) and sorbitan monolaurate. (Herein "EO" denotes ethylene oxide anda number in the parentheses is an adduct mole number.) These can be usedas a mixture. Among these examples of the nonsilicone surface activeagents, nonsilicone surface active agents having HLB of 9 to 13 arepreferable. HLB (Hydrophile-Lipophile Balance) describes the balance ofthe water affinity and the oil affinity of a surface active agent. HLBcan be controlled by the adduct mole number of ethylene oxide or themolecular weight of polyethylene glycol. Surface active agents (d) canbe selected from (d1) and/or (d2), that is, both (d1) and (d2) can beused at the same time.

The amount of surface active agents (d) used for treatment can varyaccording to the ratio of (a) and (b), the kind of (a) and theabsorption property of (c), and in general is 0.01 to 5 weight %,preferably 0.02 to 2 weight 96, and more preferably 0.03 to 1 weight %.It is preferable to have the amount for treatment of 0.01 weight % ormore since an excellent improvement of permeability and diffusibility ofa liquid can be achieved. On the other hand, it is uneconomical to havethe treatment with the amount over 5 weight % since it does not furtherimprove the property compared with the treatment conducted within therange of 0.01 to 5 weight %. Therefore 5 weight % or less is preferable.The amount of 5 weight % or less is preferable since stickiness is notgenerated.

Examples of methods of obtaining an absorbent layer by applying waterabsorbent resin (c) to fiber substrate comprising a synthetic fiber (a)and a cellulose fiber (b) optionally used include (1) a method of mixing(a), (b) and (c) simultaneously, (2) a method of mixing the mixture of(a) and (b) into (c), (3) a method of mixing the mixture of (b) and (c)to (a), (4) a method of mixing the mixture of (a) and (c) into (b), (5)a method of mixing (b) and (c) separately into (a) and (6) a method oflaminating a mixture of (a) and (b) and then sprinkling (c) thereonfollowed by laminating a mixture of (a) and (b) to form a sandwichedstructure. In these methods, (b) is an optional component used asneeded. Among these examples, methods (1), (2) and (6) are preferable.The apparatus used in these methods is not particularly limited and acommon apparatus can be used.

An absorbent layer formed accordingly is subjected to heat treatment tobe finished as an absorbent layer having an excellent shape retentionproperty in the wet state. A method of heat treatment is notparticularly limited and examples include a method of treating withhot-air, a method of passing through a heat roll and a method ofirradiating infrared ray. Temperature and duration of heat treatment canbe optionally selected as long as (a) can adhere to each other accordingto the kind of (a), the amount of (a) and the production speed ofdisposable diapers. The temperature of the heat treatment is, ingeneral, 80° to 250° C., preferably 90° to 200° C., and more preferably100° to 180° C. By having the temperature of heat treatment of 80° C. ormore, since the heating time need not be long, sufficient heatingtreatment can be conducted without the need of a large heatingapparatus, and thus it is economical. Further, it is preferable sincethe production speed of absorbent products is not lowered. Further, itis preferable to have the temperature of heat treatment of 250° C. orless, since heat deterioration of (b) or (c) is not caused.

The heating duration can be optionally selected as long as (a) canadhere to each other according to the kind of (a), the amount of (a) andthe production speed of the absorbent product. With respect to adhesionand production speed of absorbent products, the heating duration is, ingeneral, 0.5 second to 3 minutes, preferably 1 second to 1 minute.

Treatment of the absorbent layer with the surface activate agents (d) inthis invention can be conducted by any suitable method as long as theuniform application is secured. In general, an absorbent layer istreated with diluted solution of a surface active agent of approximately1 to 10 weight % concentration. By having the treatment with (d) afterforming the absorbent layer, since the surface active agent (d) can beuniformly treated to (a), (b) and (c), an excellent permeability anddiffusibiliy of a liquid can be secured. If a synthetic fiber pretreatedby (d) is used as (a), a sufficient effect can not be achieved.

This treatment can be conducted either at a stage before the heattreatment of the absorbent layer or a stage after the heat treatment.When this treatment is conducted after the heat treatment, in general,it is followed by the drying process. When this treatment is conductedbefore the heat treatment, the drying process is unnecessary.

The method and the apparatus for treating the absorbent layer with (d)are not particularly limited. Examples include a method of soaking theabsorbent layer in a solution of (d) and optionally followed bysqueezing with a mangle, a method of spraying the absorbent layer with asolution of (d) and a method of treating the absorbent layer with anoiling roll having a solution of (d) thereon.

Other compounds can be included in a solution of the above mentionedsurface active agents (d) of the present invention as long as theeffects of the present invention are not disturbed. Examples of suchcompounds include antistatic agents such as alkyl phosphate type anionsurface active agent and quaternary ammonium salt type or alkylimidazolinium salt type cationic surface active agents, emulsifiers,smoothing agents, converging agents such as other nonionic surfaceactive agents and other modified silicone surface active agents,antiseptics, perfumes and deodorants.

Absorbent layers treated with a surface active agent (d) accordingly canform a single layer or a plurality of layers with optional layers of awater-absorbent paper or a pulp, and finished as an absorbent productprovided with a liquid permeable surface sheet or a nonwoven fabric inthe surface and a liquid nonpermeable back sheet in the rear side, andfurther with gathers and application tapes for fixation. Materials andkinds of the liquid permeable surface sheets, liquid nonpermeable backsheets, gathers and application tapes, production methods of absorbentproducts are not particularly limited and materials, kinds, andproduction methods used in conventional absorbent products can beapplied.

Although it depends on the desired finished products, examples of aliquid permeable surface sheet used in the present invention includemesh-type sheets comprising polyethylene, polypropylene orpolytetrafluoroethylene, and sheets having holes with a several 100micron diameter comprising polyethylene, polypropylene orpolytetrafluoroethylene. Among these examples, a mesh type polypropylenesheet is preferable.

Although it depends on the desired finished products, examples of aliquid nonpermeable back sheet used in the present invention includepolyethylene sheets, polypropylene sheets, polytetrafluoroethylenesheets, stretched polyethylene sheets, stretched polypropylene sheetsprovided with air ventilation by stretching and stretchedpolytelytetrafluoroethylene sheets provided with air ventilation bystretching. Among these examples, stretched drawn polypropylene orpolyethylene sheets with air ventilation are preferable.

The present invention will be further illustrated with reference to theExamples and Comparative Examples. However, this invention is notlimited to these embodiments. Embodiments of disposable diapers will beexplained in Examples and Comparative Examples hereinafter, but thisinvention is not limited to disposable diapers as the absorbentproducts. But the present invention can be applied to embodiments ofother absorbent products such as sanitary napkins and incontinence pads.Absorption rate, diffusion area, surface dryness and shape retentionproperty are evaluated in the below mentioned methods. "%" denotesweight % hereinafter unless otherwise specified.

Absorption rate: An acryl plate having the size same as a disposablediaper having the weight of 0.5 kg with a cylinder having a bore of 3 cmin the center is located on the disposable diaper and a 4.5 kg load isapplied on the acryl plate to provide a total load of 5 kg. The acrylplate is provided with a hole in the center to discharge a liquid fromthe above mentioned cylinder. 80 ml of artificial urine colored with ablue ink is poured in the cylinder to have the disposable diaper absorbit. After 30 minutes, a further 80 ml of artificial urine is poured forthe second time. After 30 minutes, a further 80 ml of artificial urineis poured similarly for the third time and the absorption time ismeasured to be determined as the absorption rate.

Diffusion area: After the third pour of the artificial urine andmeasuring the absorption rate, the area in which the artificial urine isabsorbed and expanded, which is colored to be blue, is measured anddetermined as the diffusion area.

Surface dryness: After measuring the diffusion area, the surface drynessof disposable diapers in the area where the artificial urine is pouredis judged by touching by 10 panelists and evaluated according to thebelow mentioned four grades. The average of the evaluation is determinedas the surface dryness.

⊚: Good dryness

◯: Satisfactory dryness although slightly moist

Δ: Moist state with a little dryness

x: Wet state without dryness

Shape retention property: After 30 minutes from the third pour of theartificial urine, the disposable diaper is twisted by hand and the shaperetention property after 5 minutes is evaluated by visual observationand evaluated according to the below mentioned three grades.

⊚: Restored the original shape

◯: Almost restored the original shape satisfactorily

x: The shape is destroyed

Absorbent layer (A)

A mixture prepared by mixing 30 weight parts of a sheath & core typeconjugate fiber having polypropylene as the core component andpolyethylene as the sheath component ("ES Fiber EAC" produced by ChissoCorporation; melting point of the low-melting point component: 110° C.),70 weight parts of fluff pulp and 50 weight parts of crosslinked sodiumacrylate-based water absorbent resin (absorbency under pressure-freestate: 50 g/g, absorbency under loading: 28 g/g, gel elastic modulus:92,000 dyne/cm², average particle size 480 μm) in an air blender wasuniformly laminated to have a weight of approximately 400 g/m² andpressed for 90 seconds with 5 kg/cm² pressure. Then the absorbent layerwas cut in a 14 cm×36 cm rectangular shape and sprayed with 10 parts of1% aqueous solution of polyoxyethylene modified dimethylpolysiloxane("SANSILICON M-84" manufactured by Sanyo Chemical Industries, Ltd.,containing approximately 50% by weight of polyoxyethylene groups andhaving an average molecular weight of approximately 1,000,), followed byhot air treatment at 130° C. for 3 minutes to obtain the absorbent layer(A) of the present invention.

Absorbent layers (B) and (C)

Except that the ratio (weight ratio) of the conjugate fiber, the fluffpulp and the water absorbent resin was changed as mentioned below, theabsorbent layer (B) and the absorbent layer (C) were obtained by thesame procedure as the absorbent layer (A).

Absorbent layer (B): conjugate fiber/fluff pulp/absorbent resin=50/50/70

Absorbent layer (C): conjugate fiber/fluff pulp/absorbent resin=100/0/100

Absorbent layer (D)

Except that 25 weight parts of the 1% aqueous solution ofpolyoxyethylene modified dimethyl polysiloxane was sprayed instead of 10weight parts in the absorbent layer (A), the absorbent layer (D) wasobtained by the same procedure as the absorbent layer (A).

Absorbent layers (E) and (F)

Except that random copolymers of polyoxyethylene-polyoxypropylene(copolymerization mole ratio: oxyethylene/oxypropylene=75/25) modifieddimesyl polysiloxane (average molecular weight: approximately 2,500,percentage content of polyoxyethylene group: approximately 40%) was usedinstead of polyoxyethylene modified dimethyl polysiloxane in theabsorbent layers (A) and (D), the absorbent layer (E) and the absorbentlayer (F) were obtained by the same procedure as the absorbent layers(A) and (D) respectively.

Absorbent layer (G)

Except that the same amount of an eccentric core-sheath type conjugatefiber having polypropylene as the core component and polyethylene as thesheath component ("ES Fiber EA" produced by Chisso Corporation; meltingpoint of the low-melting point component: 110° C.) was used instead ofthe sheath & core type conjugate fiber ("ES Fiber EAC" produced byChisso Corporation; melting point of the low-melting point component:110° C.), the absorbent layer (G) was obtained by the same procedure asthe absorbent layer (A).

Absorbent layer (H)

Except that the same amount of surface crosslinked starch-sodiumacrylate copolymers-based water absorbent resin particles (absorbencyunder pressure-free state: 58 g/g, absorbency under loading: 38 g/g, gelelastic modulus: 105,000 dyne/cm², average particle size: 350 μm) wasused instead of the crosslinked sodium polyacrylate-based waterabsorbent resin (absorbency under pressure-free state: 50 g/g,absorbency under load: 28 g/g, gel elastic modulus: 92,000 dyne/cm²,average particle size: 480 μm), the absorbent layer (H) was obtained bythe same procedure as the absorbent layer (A).

Comparative absorbent layer (f)

Except that polyoxyethylene modified dimethyl polysiloxane was notsprayed on the absorbent layer, the comparative absorbent layer (f) wasobtained by the same procedure as the absorbent layer (A).

Comparative absorbent layer (g)

Except that the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=30/70/50 in the comparative absorbent layer (f) waschanged to the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=100/0/100, the comparative absorbent layer (g) wasobtained by the same procedure as the comparative absorbent layer (f).

Comparative absorbent layers (h) to (j)

Except that the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=30/70/50 in the absorbent layer (A) of the presentinvention was changed to the below mentioned weight ratio of conjugatefiber/fluff pulp/absorbent resin, the comparative absorbent layers (h)to (j) were obtained by the same procedure as the absorbent layer (A).

Comparative absorbent layer (h): conjugate fiber/fluff pulp/absorbentresin=0/100/50

Comparative absorbent layer (i): conjugate fiber/fluff pulp/absorbentresin=10/90/50

Comparative absorbent layer (j): conjugate fiber/fluff pulp/absorbentresin=50/50/350

Comparative absorbent layer (k)

Except that polyoxyethylene modified dimesyl polysiloxane (averagemolecular weight: approximately 1,000, percentage content ofpolyoxyethylene group: approximately 20%) was used instead ofpolyoxyethylene modified dimethyl polysiloxane in the absorbent layer(A) in the present invention, the comparative absorbent layer (k) wasobtained by the same procedure as the absorbent layer (A).

EXAMPLES 1 TO 8

Model disposable diapers were prepared by cutting the absorbent layers(A) to (H) of the present invention in a 14 cm×36 cm rectangular shaperespectively, applying water absorbent paper having the same size as theabsorbent layer to both sides of the absorbent layer and locating apolyethylene sheet commonly used in disposable diapers on the rear sideand a nonwoven fabric on the surface side. Evaluation results of thesemodel disposable diapers in terms of absorption rate, diffusion area,surface dryness and shape retention property are described in Table 1.

COMPARATIVE EXAMPLES 1 TO 6

Comparative model disposable diapers were prepared with the comparativeabsorbent layers (f) to (k) by the same process as the Examples.Evaluation results of these model disposable diapers in terms ofabsorption rate, diffusion area, surface dryness and shape retentionproperty are described in Table 1.

                  TABLE 1                                                         ______________________________________                                                                            shape                                              absorption rate                                                                        diffusion                                                                              surface  retention                                          (second) area (cm.sup.2)                                                                        dryness  property                                  ______________________________________                                        Example 1      83         297    ⊚                                                                     ∘                                 2      84         283    ⊚                                                                     ⊚                              3      88         275    ⊚                                                                     ⊚                              4      49         310    ⊚                                                                     ∘                                 5      85         288    ⊚                                                                     ∘                                 6      53         303    ⊚                                                                     ∘                                 7      80         292    ⊚                                                                     ∘                                 8      77         292    ⊚                                                                     ∘                         Comparative                                                                           1      170        185    x      ∘                         Example 2      224        175    x      ⊚                              3      61         285    ∘                                                                        x                                             4      77         281    ∘                                                                        x                                             5      280        186    ∘                                                                        x                                             6      156        198    Δ                                                                              ∘                         ______________________________________                                    

Absorbent layer (I)

A mixture prepared by mixing 30 weight parts of a sheath & core typeconjugate fiber having polypropylene as the core component andpolyethylene as the sheath component ("ES Fiber EAC" produced by ChissoCorporation; melting point of the low-melting point component: 110° C.),70 weight parts of fluff pulp and 50 weight parts of crosslinked sodiumacrylate-based water absorbent resin (absorbency under pressure-freestate: 50 g/g, absorbency under loading: 28 g/g, gel elastic modulus:92,000 dyne/cm², average particle size 480 μm) in an air blender wasuniformly laminated to have a weight of approximately 400 g/m² andpressed for 90 seconds with 5 kg/cm² pressure. Then the absorbent layerwas cut in a 14 cm×36 cm rectangular shape and sprayed with 10 parts of1% aqueous solution of a nonionic surface active agent, polyoxyethyleneoleyl-cetyl ether ("Emulmin 60" manufactured by Sanyo ChemicalIndustries, Ltd.; HLB 10.3), followed by hot air treatment at 130° C.for 3 minutes to obtain the absorbent layer (I) of the presentinvention.

Absorbent layers (J) and (K)

Except that the ratio (weight ratio) of the conjugate fiber, the fluffpulp and the water absorbent resin was changed as mentioned below, theabsorbent layer (J) and the absorbent layer (K) were obtained by thesame procedure as the absorbent layer (I).

Absorbent layer (J): conjugate fiber/fluff Pulp/absorbent resin=50/50/70

Absorbent layer (K): conjugate fiber/fluff pulp/absorbent resin=100/0/100

Absorbent layer (L)

Except that 25 weight parts of the 1% aqueous solution ofPolyoxyethylene oleyl-cetyl ether was sprayed instead of 10 weight partsin the absorbent layer (I), the absorbent layer (L) was obtained by thesame procedure as the absorbent layer (I).

Absorbent layers (M) to (P)

Except that the below mentioned surface active agents were used insteadof polyoxyethylene oleyl-cetyl ether in the absorbent layer (I), theabsorbent layers (M) to (P) were obtained by the same procedure as theabsorbent layer (I).

Absorbent layer (M): Polyoxyethylene oleyl-cetyl ether (a nonionicsurface active agent "Emulmin 40" produced by Sanyo Chemical Industries,Ltd.; HLB 8.0)

Absorbent layer (N): Polyoxyethylene nonylphenyl ether (a nonionicsurface active agent "Nonipol 40" produced by Sanyo Chemical Industries,Ltd.; HLB 8.9)

Absorbent layer (O): sorbitan monolaurate-EO 4 mole (HLB 8.6)

Absorbent layer (P): polyoxyethylene lauryl-myristyl ether (a nonionicsurface active agent "Nonipol Soft SS-50" produced by Sanyo ChemicalIndustries, Ltd.; HLB 10.6)

Absorbent layer (Q)

Except that the same amount of an eccentric core-sheath type conjugatefiber having polypropylene as the core component and polyethylene as thesheath component ("ES Fiber EA" produced by Chisso Corporation; meltingpoint of the low-melting point component: 110° C.) was used instead ofthe sheath & core type conjugate fiber ("ES Fiber EAC" produced byChisso Corporation; melting point of the low-melting point component:110 ° C.), the absorbent layer (Q) was obtained in the same procedure asthe absorbent layer (I).

Absorbent layer (R)

Except that the same amount of surface crosslinked starch-sodiumacrylate copolymers-based water absorbent resin particles (absorbencyunder pressure-free state: 58 g/g, absorbency under loading: 36 g/g, gelelastic modulus: 105,000 dyne/cm², average particle size: 350 μm) wasused instead of the crosslinked sodium polyacrylate-based waterabsorbent resin (absorbency under pressure-free state: 50 g/g,absorbency under load: 28 g/g, gel elastic modulus: 92,000 dyne/cm²,average particle size: 480 μm), the absorbent layer (R) was obtained bythe same procedure as the absorbent layer (I).

Comparative absorbent layer (m)

Except that polyoxyethylene oleyl-cetyl ether was not sprayed on theabsorbent layer, the comparative absorbent layer (m) was obtained by thesame procedure as the absorbent layer (I).

Comparative absorbent layer (n)

Except that the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=30/70/50 in the comparative absorbent layer (m) waschanged to the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=100/0/100, the comparative absorbent layer (n) wasobtained by the same procedure as the comparative absorbent layer (m).

Comparative absorbent layers (o) to (q)

Except that the weight ratio of conjugate fiber/fluff pulp/waterabsorbent resin=30/70/50 in the absorbent layer (I) of the presentinvention was changed to the below mentioned weight ratio of conjugatefiber/fluff pulp/absorbent resin, the comparative absorbent layers (o)to (q) were obtained by the same procedure as the absorbent layer (I).

Comparative absorbent layer (o): conjugate fiber/fluff pulp/absorbentresin=0/100/50

Comparative absorbent layer (p): conjugate fiber/fluff pulp/absorbentresin=10/90/50

Comparative absorbent layer (q): conjugate fiber/fluff pulp/absorbentresin=50/50/350

Comparative absorbent layers (r) and (s)

Except that surface active agents having the below mentioned HLBs wereused instead of polyoxyethylene oleyl-cetyl ether having HLB 10.3 of theabsorbent layer (I) of the present invention, the comparative absorbentlayers (r) and (s) were obtained by the same procedure as the absorbentlayer (I).

Comparative absorbent layer (r): polyoxyethylene nonylphenyl ether (anonionic surface active agent "Nonipol 20" produced by Sanyo ChemicalIndustries, Ltd.; HLB 5.7)

Comparative absorbent layer (s): polyoxyethylene nonylphenyl ether (anonionic surface active agent "Nonipol 120" produced by Sanyo ChemicalIndustries, Ltd.; HLB 14.8)

EXAMPLES 9 TO 18

Model disposable diapers were prepared by cutting the absorbent layers(I) to (R) of the present invention in a 14 cm×36 cm rectangular shaperespectively, applying water absorbent paper having the same size as theabsorbent layer to both sides of the absorbent layer and locating apolyethylene sheet commonly used in disposable diapers on the rear sideand a nonwoven fabric on the surface side. Evaluation results of thesemodel disposable diapers in terms of absorption rate, diffusion area,surface dryness and shape retention property are described in Table 2.

COMPARATIVE EXAMPLES 7 TO 13

Comparative model disposable diapers were prepared with the comparativeabsorbent layers (m) to (s) by the same process as Examples. Evaluationresults of these model disposable diapers in terms of absorption rate,diffusion area, surface dryness and shape retention property aredescribed in Table 2.

                  TABLE 2                                                         ______________________________________                                                                            shape                                              absorption rate                                                                        diffusion                                                                              surface  retention                                          (second) area (cm.sup.2)                                                                        dryness  property                                  ______________________________________                                        Example  9     83         277    ⊚                                                                     ∘                                 10     78         271    ⊚                                                                     ⊚                              11     80         264    ⊚                                                                     ⊚                              12     66         294    ⊚                                                                     ∘                                 13     108        259    ⊚                                                                     ∘                                 14     97         262    ⊚                                                                     ∘                                 15     90         258    ⊚                                                                     ∘                                 16     84         270    ⊚                                                                     ∘                                 17     85         280    ⊚                                                                     ∘                                 18     82         268    ⊚                                                                     ∘                         Comparative                                                                            7     170        185    x      ∘                         Example  8     231        177    x      ⊚                               9     64         280    ∘                                                                        x                                             10     71         268    ∘                                                                        x                                             11     220        182    ∘                                                                        x                                             12     153        195    Δ                                                                              ∘                                 13     260        191    x      ∘                         ______________________________________                                    

Absorbent products of the present invention have the followingcharacteristics and advantageous effects.

1 Excellent absorption property and absorption rate even in the case ofrepetitive absorptions.

2 Good liquid diffusion to provide excellent surface dryness afterabsorption.

3 Reduced leakage of the absorbed liquid.

4 Excellent shape retention property to external force such as shearing,compression and wrinkle by the wearer's movement in the moist condition.

5 Excellent unity of the absorbent resin and the fiber substrate

Since the absorbent products of the present invention have the abovementioned effects, they are preferable for the application in disposablediapers (disposable diapers for infants or for adults), and inparticular, in thin-type disposable diapers that have a large ratio ofthe water absorbent resin/fiber material.

Further, the absorbent products of the present invention are preferablefor the application in other hygienic materials such as sanitarynapkins, incontinence pads, mother's milk pads, underpads for medicaloperations, childbirth mats, dressing materials for injury protection,and pet sheets as well as various kinds of absorbent sheets such asfreshness retaining sheets, drip absorbent sheets, anti-dewing sheets,paddy seedling sheets, concrete curing sheets, oil/water separatingsheets and fire extinction sheets.

What is claimed is:
 1. An absorbent product comprising a liquidpermeable surface sheet, a liquid nonpermeable back sheet and anabsorbent layer located therebetween, wherein the absorbent layercomprises a water nonswellable synthetic fiber (a) or the combination ofthe synthetic fiber (a) and a cellulose fiber (b), and a water-absorbentresin (c) with the weight ratio of (a):(b) being (100 to 20):(0 to 80)and the percentage content of (c) based on the weight sum of (a), (b)and (c) is 25 to 75% by weight, the absorbent layer being treated with apolyoxyalkylene-modified silicone surface active agent (d1).
 2. Theabsorbent product according to claim 1, wherein the synthetic fiber (a)is at least one selected from a group consisting of polyolefin fibers,polyester fibers and a conjugate fiber thereof.
 3. The absorbent productaccording to claim 1, wherein the absorbent resin (c) is a powderyhydrophilic crosslinked polymer derived from acrylic acid salt and/oracrylic acid as a main monomer component for the polymer.
 4. Theabsorbent product according to claim 1, wherein the absorbent resin (c)is capable of absorbing 45 to 75 times its weight of physiologicalsaline under a pressure free state, and is capable of absorbing 25 to 50times its weight of physiological saline under loading and has a gelelastic modulus of 30,000 to 200,000 dyne/cm².
 5. The absorbent productaccording to claim 1, wherein the amount of the polyoxyalkylene modifiedsilicone surface active agent (d1) used for treatment is 0.01 to 5% byweight based on the weight sum of (a), (b) and (c).
 6. The absorbentproduct according to claim 1, wherein the polyoxyalkylene modifiedsilicone surface active agent (d1) is a polyoxyethylene modifieddimethyl polysiloxane having a molecular weight of 500 to 10,000 and apercentage content of a polyoxyethylene group of 40 to 60% by weight.